Conventionally, in a pneumatic tire (hereinafter, referred to as tire) mounted on a passenger vehicle, for example, a method for forming a plurality of circumferential grooves in a tread has been widely used in order to ensure a water drainage performance on a wet road surface.
Further, there is known a tire in which a plurality of protrusions to be inclined relative to a tire circumferential direction are formed on a groove bottom of a circumferential groove in order to aggressively drain rainwater that has entered such a circumferential groove (for example, Patent Literature 1). According to such a tire, a spiral water flow is hardly generated in the rainwater that has entered the circumferential grooves, resulting in the improvement of a water drainage performance.
In recent years, along with an introduction of an electric vehicle or a hybrid automobile in which both an internal combustion engine and an electric motor are used, a further reduction of noise generated by a tire is demanded. Further, even in an automobile mounted thereon with an internal combustion engine, along with a reduction of noise generated by the automobile itself, a further reduction of noise generated by a tire is demanded than ever. Main examples of the noise generated by a tire include a pattern noise resulting from a tread pattern (pitch noise) and a road noise resulting from an unevenness on a road surface. As a method of reducing a pattern noise, it is possible to consider reducing a lug groove component in a tread.
However, even with the tire in which a lug groove component is thus reduced, it is necessary to ensure a water drainage performance at least equal to that of a conventional tire.